1. Field of the Invention
The present invention relates in general to an optical fiber routing device and more particularly to a device for routing optical fibers for interconnection with a printed circuit board.
2. Description of the Related Art
The use of optical fibers to transmit high speed data signals is becoming more and more common. Glass fibers are used to route transmit signals long distances, perhaps between countries. Polymeric fibers are used for much shorter distances, where signal attenuation is not a problem. For example, in a telephone switching office, the various switching components are split onto different printed circuit boards. Polymeric optical fibers may be used to route the signals between the different circuit boards.
FIG. 1 is a perspective view of a conventional printed circuit board 8 and the apparatus for interconnecting an optical fiber therewith. Printed circuit board 8 is generally placed in a shelf or rack alongside other such circuit boards. Electrical contacts 12 connect with corresponding contacts at the back of the shelf. Circuit board 8 is secured into place with a pair of locking devices 14.
In FIG. 1, optical fibers are first received by reception ports 2. Then, optical fiber pieces 4 are used for transferring signals between reception ports 2 and electro-optical converters 6. The optical fiber pieces 4 generally come in three and six foot lengths with connectors 5 provided at the ends thereof. However, printed circuit board 8 may have a width of only several inches. To accommodate for the extra length in the optical fiber pieces 4, they are channelled around the circuit board 8 as shown in FIG. 1. Clips 10 are used to secure the optical fiber pieces 4 to the printed circuit board 8.
With increasing desire for greater integration, the space on circuit board 8 has become expensive. To secure the clips 10 to circuit board 8, holes, perhaps four or more holes, must be drilled through the circuit board 8. With four holes each having a three eights inch diameter, this consumes about 0.44 square inches of space. The components on the circuit board are connected together with traces above and within the board. The length of a trace may be limited by signal degradation or loss of speed problems associated with longer lengths. Wherever a hole appears in the circuit board for a clip 10, a trace cannot be placed. If the trace has a limited length, placement of the components connected by the trace can be complicated. Furthermore, with the configuration shown in FIG. 1, the optical fiber pieces 4 run immediately adjacent to the printed circuit board 8. Only small components can fit under optical fiber 4. Large components would disturb the routing. That is, the optical fiber 4 has a minimum bend radius, and if bent beyond the minimum bend radius, signal degradation will result. Nine linear inches (the circumference of the circle of fiber) of fiber may be required to loop the fiber around to take up slack without bending beyond the minimum bend radius. Over this distance, the height of components is limited.
Designing where to place clips 10 also poses a problem. If it is necessary to move one clip 10 because of a trace intersection, for example, all other clips 10 must be also moved. To simultaneously find four acceptable places for all clips 10 represents a problem.
Once the printed circuit board 8 is designed with the layout of the components and the holes for clips 10, assembly can be difficult. To assemble the device, the fiber optic pieces 4 are generally routed, by hand, through the clips 10. As mentioned above, the optical fiber pieces cannot be bent beyond the minimum bend radius. Whether this requirement is satisfied depends on the individual operator doing the assembly.
As an alternative to the configuration shown in FIG. 1, it has been proposed to mount clips 10 to a unit which in turn is mounted to the printed circuit board 8. The purpose of this device is to minimize the number of holes that must be formed through printed circuit board 8. However, this device also increases the height above the printed circuit board 8 at which the optical fiber pieces 4 are routed. In FIG. 1, reference numerals 11 represents standoffs. A smaller circuit board is mounted to the standoffs 11. If a separate device is used for mounting clips 10, the height of the routing extends beyond the bottom of standoffs 11 and interferes with connection of the smaller circuit board.